1. Field of the Invention
The present invention relates to clustering and virtualization technology, and more particularly to a shared-nothing virtual cluster formation that eliminates shared hardware.
2. Description of the Related Art
The following definitions are provided for this disclosure with the intent of providing a common lexicon. A “physical” device is a material resource, such as, for example, a server, a network switch, memory devices, a disk drive, etc. Even though physical devices are discrete resources, they are not inherently unique. For example, random access memory (RAM) devices and a central processing unit (CPU) in a physical server may be interchangeable between like physical devices. Also, network switches may be easily exchanged with minimal impact. A “logical” device is a representation of a physical device to make it unique and distinct from other physical devices. For example, every network interface has a unique media access control (MAC) address. A MAC address is the logical unique identifier of a physical network interface card (NIC). A “traditional” device is a combined logical and physical device in which the logical device provides the entire identity of a physical device. For example, a physical NIC has its MAC address permanently affixed so the physical device is inextricably tied to the logical device.
A “virtualized” device breaks the traditional interdependence between physical and logical devices. Virtualization allows logical devices to exist as an abstraction without being directly tied to a specific physical device. Simple virtualization can be achieved using logical names instead of physical identifiers. For example, using an Internet Uniform Resource Locator (URL) instead of a server's MAC address for network identification effectively virtualizes the target server. Complex virtualization separates physical device dependencies from the logical device. For example, a virtualized NIC could have an assigned MAC address that exists independently of the physical resources managing the NIC network traffic.
A cluster includes at least two computers or servers communicatively coupled together and to a shared hardware disk drive that stores shared data. Clustering may be implemented as Active/Active (A/A) or Active/Passive (A/P). For the A/A configuration, the servers are active and operating to handle respective loads. The shared data (called a “quorum”) stored on the shared drive is constantly shared between the two servers. In the event of failure of either server in a two-server cluster for the A/A configuration, the other server automatically resumes responsibility for the entire load previously shared by both. For the A/P configuration, one of the servers is the “active” node whereas the other server is the “passive” node. The active node handles the entire cluster load while the passive node remains in a standby state or the like. In the event of failure of the active server in the A/P configuration, a “failover” occurs in which the passive server is switched or otherwise “promoted” to active mode to resume handling the cluster load. In this manner, the passive server operates as a fail-safe mechanism for the active server.
A link is provided between the clustered servers to detect failure and to facilitate a failover event. The link may perform several functions, such as monitoring the status of the active server, detecting failure of the active server and providing failure notification. The link may further operate to coordinate failover, if necessary. In the event of failure, the active server is “demoted” to passive status and the passive server is promoted to active status to effectuate the failover.
A traditional virtual cluster employs a virtualization layer on top of physical devices. The virtual cluster is similar to the physical cluster in that it includes two computers or servers communicatively coupled together and a link that detects a failover condition. In the virtual case, however, a first virtual server is implemented on a first underlying physical server and a second virtual server is implemented on a second physical server. A communication link is provided between the virtual servers and with a shared virtual drive implemented on a third physical device. The shared virtual drive stores shared data for the virtual servers of the virtual cluster.
Operation of the virtual cluster is similar to its physical counterpart. For the A/P configuration in which the first virtual server is the active node, in the event of failure of the first physical server, the passive virtual server is promoted to active mode to resume handling of the cluster load. In this case, a drive image or the like describing or otherwise defining characteristics of the virtual server is stored on the virtual drive, and is employed to create or otherwise power up the virtual server during the failover event.
The traditional cluster configurations have several disadvantages. Both servers require access to the shared drive, which results in an expensive and complicated structure. The traditional clusters have physical limitations in that the physical separation between the physical servers and physical devices storing the shared data is a limiting factor. Also, the additional shared hardware for the shared drive results in an additional point of failure. The shared data configuration is expensive and requires special software and configuration. The operating system (OS) of both servers must support clustering. Application software may need to support clustering. For the virtual configuration, the virtualization software must support clustering or otherwise be configured to handle the clustered structure. The shared drive (physical or virtual) must be pre-configured to support clustering. The clustering portions, including the servers and drives, are not easily replaced or substituted.
There is a need in the industry for a more flexible and less complicated cluster configuration.